net: relax rcvbuf limits

skb->truesize might be big even for a small packet.

Its even bigger after commit 87fb4b7b533 (net: more accurate skb
truesize) and big MTU.

We should allow queueing at least one packet per receiver, even with a
low RCVBUF setting.

Reported-by: Michal Simek <monstr@monstr.eu>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 6 insertions, 10 deletions

diff --git a/include/net/sock.h b/include/net/sock.h
index abb6e0f0c3c3..32e39371fba6 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -637,12 +637,14 @@ static inline void __sk_add_backlog(struct sock *sk, struct sk_buff *skb)
 
 /*
  * Take into account size of receive queue and backlog queue
+ * Do not take into account this skb truesize,
+ * to allow even a single big packet to come.
  */
 static inline bool sk_rcvqueues_full(const struct sock *sk, const struct sk_buff *skb)
 {
         unsigned int qsize = sk->sk_backlog.len + atomic_read(&sk->sk_rmem_alloc);
 
-        return qsize + skb->truesize > sk->sk_rcvbuf;
+        return qsize > sk->sk_rcvbuf;
 }
 
 /* The per-socket spinlock must be held here. */
diff --git a/net/core/sock.c b/net/core/sock.c
index 4ed7b1d12f5e..b23f174ab84c 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -288,11 +288,7 @@ int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
         unsigned long flags;
         struct sk_buff_head *list = &sk->sk_receive_queue;
 
-        /* Cast sk->rcvbuf to unsigned... It's pointless, but reduces
-           number of warnings when compiling with -W --ANK
-         */
-        if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
-            (unsigned)sk->sk_rcvbuf) {
+        if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf) {
                 atomic_inc(&sk->sk_drops);
                 trace_sock_rcvqueue_full(sk, skb);
                 return -ENOMEM;
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 82a6f34d39d0..3891702b81df 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1630,8 +1630,7 @@ static int packet_rcv(struct sk_buff *skb, struct net_device *dev,
         if (snaplen > res)
                 snaplen = res;
 
-        if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
-            (unsigned)sk->sk_rcvbuf)
+        if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
                 goto drop_n_acct;
 
         if (skb_shared(skb)) {
@@ -1762,8 +1761,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
         if (po->tp_version <= TPACKET_V2) {
                 if (macoff + snaplen > po->rx_ring.frame_size) {
                         if (po->copy_thresh &&
-                                atomic_read(&sk->sk_rmem_alloc) + skb->truesize
-                                < (unsigned)sk->sk_rcvbuf) {
+                            atomic_read(&sk->sk_rmem_alloc) < sk->sk_rcvbuf) {
                                 if (skb_shared(skb)) {
                                         copy_skb = skb_clone(skb, GFP_ATOMIC);
                                 } else {